Re: Sky People's solar system
| From: | Christophe Grandsire <christophe.grandsire@...> |
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| Date: | Wednesday, January 20, 1999, 9:43 |
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At 10:58 19/01/99 -0500, you wrote:
>On Tue, 19 Jan 1999, Christophe Grandsire wrote:
>
>> I know
>> also that you can't place planets wherever you want (I think the average
>> radii of the orbits in our solar system follows a series of numbers that I
>> don't remember (but I remember having seen it!)) and I want to make my
>> solar system as "natural" as possible. So I need the average radii of the
>> planets' orbits, and the corresponding time of revolution. If anyone knows
>> the relation...
>
>I have only one nitpick with this: there's no such thing as a "natural"
>(i.e., normal!) solar system. We only know one real well (hence I suppose
>the idea of an ideal or natural solar system!); and none of the others
>that are being studied are at all like ours, beyond the basics. One I can
>think of off hand has a gas giant up close to the star, and smaller
>planets further out: in contravention of what seems "natural" to us, whose
>gas giants are well away from the star. Thus, I think there is no real
>harm in placing the planets more or less where you wish!
>
>Besides, how different would our astronomy be if _we_ had a whopping great
>gas giant right next door, perhaps in place of Venus!
>
>> As far as I've designed the solar system, it has:
>>
>> - a sun (only ne) that is just a bit hotter than ours, so habitablme
>> planets must be a little farther than our Earth from the sun.
>
>Quite plausible; I believe current thought is that Venus and Mars are at
>the inner and outer areas of the "life belt". At least the sort of life
>_we_ are!
>
As the Sky People are a kind of life very close to us, it was mandatory.
>>
>> - 13 planets (in fact 14 as there is a double one) and 2 asteroid belts
>> which are placed, from the nearest to the farthest from the sun:
>
>The more the merrier!
>
>>
>> - the smallest planet of the system, even smaller than our
>> Mercury. It's so near to the sun that it is totally invisible at eyes'
>> sight;
>>
>> - a double planet, the bigger the size of Mars, the smaller just
>> slightly smaller. No atmosphere (to close to the sun), but visible.
>
>Don't be too quick to assume that nearness to the star = no atmosphere.
>Mercury has a sodium-helium-hydrogen atmosphere. Thin to be sure, but
>there!
>
Is it really an atmosphere or some gas rejected by the sun and captured by
the gravity of Mercury? I mean, if its composition keeps stable whatever
the activity of the sun, it's an atmosphere. If not, I can't name it an
atmosphere.
>>
>> - a planet as big as Earth, with no moon. In the habitable zone
>> but too hotter to have life. The biggest volcanic activity of the solar
>> system (makes it inhabitable).
>
>Somewhat like Venus then.
But darker.
>
>>
>> - the planet of the Sky People, slightly bigger and denser than
Earth
>> (just enough to have a gravity of 1.1 instead of 1). Exactly in the midddle
>> of the habitable zone, so farther to its sun than Earth to its (it will
>> make a year of 450 Earth days or so I think). 2 moons, one smaller than the
>> Moon, the other bigger. I want them to be placed to have the same apparent
>> radius as the sun (to have more possibilities of eclipses (sp?)) and I need
>> their time of revolution around the planet to make a "small month" and a
>> "big month" (for the Sky People's calendar). If anyone can help...
>
>You might want to make them (the moons) rather larger than the solar
>radius, for as time passes, planetary rotation slows and the moons will
>move further away (as ours is). Thus, if the moons start out large and
>somewhat close to the planet, by the time the Sky People pop into History,
>the moons will be the right size and distance from the planet for complete
>eclipses.
>
>>
>> - the first asteroid belt, with the biggest asteroids (some of
>> the size of the moons of the planet of the Sky People).
>>
>
>> - a Neptune-like (or Uranus-like) gas giant planet. A dozen of
>> moons. A very small ring.
>
>I read recently that planetary rings and small moon(let)s go hand in hand.
>I think it had to do with the planet's gravity ripping bits off the moons,
>which form rings.
I've heard that too. That's why my gas giants have all rings.
>
>>
>> - a kind of hybrid, to big to be a rock planet, to small to be a
gas
>> giant. A kind of very big rock planet with a very thick atmosphere. A
>> fourth as big as the Neptune-like planet. five moons.
>>
>> - a gas giant with very thick rings, a little bigger than Saturn.
>> Something like 30 moons.
>>
>
>> - the biggest planet of the system, a tenth bigger than Jupiter.
>> 23 moons and a strange system of _two_ perpendicular rings, an
>> equatorial ring and a polar one. As strange as it appears, the polar
>> ring is stable. The last visible planet of the system.
>
>Very odd and strange! Perhaps astronomers will eventually find turbulent
>clouds of smashed debris where the two ring systems meet?
>
Surely!
>>
>> - the second asteroid belt, with much smaller asteroids (due to
both
>> planets surrounding the belt).
>>
>> - another gas Neptune-like gas giant, 10 moons.
>>
>> - a solitary little rock and icy planet, maybe an ex-moon of the
next
>> planet (very possible as its orbit cuts the orbit of this planet). It has a
>> small volcanic activity, hence a light atmosphere. No moon.
>>
>> - another gas giant, bigger than Neptune, with small rings. 9
>> moons or so.
>>
>> - another rock and icy planet the size of Earth. No atmosphere.
One moon
>> the size of the Moon.
>>
>> - the last planet of the system, a Neptune-like gas giant with
>> only two moons.
>
>Why not a methane or ammonia atmosphere? Most of our planets and
>moons seem to have some kind of atmosphere.
>
>Does your system have an Oort Cloud or similar with which to rain comets
>on your planets?
>
I'll think of it, but I think I'll add one. Comets are so beautiful!
>>
>> As you can see, my solar system is already well defined. I need
>> only to find the average radii of the orbits and the time of revolution
>> for each planet (and the ones for the two moons of the Sky People's
>> planet). That's why I need your help. Does anyone know at least those
>> parameters for our own solar system (I'll extrapolate from it)?
>
>In addition to distance from the Sun, I thought I'd add a couple of other
>interesting data for you to consider: avg. dist. from Sun; length of year;
>inclination of orbital plane (w/r to plane of solar system); inclination
>of planetary rotation to that planet's orbital plane; temp. range.
>
That's why I needed help.
>1AU = 149,600,000km (approx.)
>273 degrees K = a balmy 0 deg C
>
> distance year inclin. inclin. temp.
> of plane to plane deg K
>Merc.: 0.037AU 88days 7d00m 0d00m 100-700
>Venus: 0.723AU 225 3d23m 177d18m 700
>Earth: 1.000AU 365 0d00m 23d27m 250-300
>Mars : 1.520AU 687 1d51m 25d12m 210-300
>Jup. : 5.202AU 4333 1d18m 3d07m 110-150
>Sat. : 9.540AU 10759 2d29m 26d44m 95
>Uran.: 19.280AU 30685 0d46m 97d52m 58
>Nept.: 30.220AU 60188 1d46m 29d34m 56
>Pluto: 39.830AU 90700 17d07m 98d00m 40
>
>Padraic.
>
Thank you for your information. It will be very useful.
John Cowan wrote:
>
>You can put the planets and satellites anywhere you want: no law
>dictates their periods of revolution or rotation. The only law
>you must observe is the harmonic law: p^2/r^3 must be constant,
>where p is the period of revolution and r is the radius of the
>orbit.
>
>The constant is (4*pi^2)/(M*G) where M is the mass of the
>primary body (the sun for a planet, the planet for a satellite)
>and G is the gravitational constant,
>approximately 6.67259*10^-11 m^3/kg sec^2. This version of the
>law does not hold if the mass of the planet/satellite is not
>negligible with respect to the mass of the sun/planet, which is most
>unlikely.
>
>So you can choose either period of revolution or distance, but not both.
>Rotations can be anything you want.
Thanks, that was the law I didn't remember. Now I'll be able to make the
length of the year.
>Yes, there is Bode's Law (or the Bode-Titius rule), but it's a purely
>empirical relationship, and we have no real reason to think it
>applies to other stellar systems.
>
>But if you want to use it, it predicts that planets are found at
>each value of 3n+4, where n = 0, 1, 2, .... It works fairly well
>for the Solar System if you count Mercury as planet 0, ...,
>Ceres as planet 4, Jupiter as planet 5, etc. Neptune however is
>completely off from Planet 8, with a distance of 301 arbitrary units
>instead of 388. (Pluto, generally thought to be an escaped moon, is
>at 394.)
>
>The Bode's Law web page
>(
http://www.itsnet.com/home/bmager/public_html/pluto/bodeslaw.html)
>says:
>
># The Titius-Bode Rule remains an interesting coincidence, for which
># no one has offered a satisfactory explanation.
>